Lithography system and projection method

ABSTRACT

The inventions relates to a lithography system in which an electronic image pattern is delivered to a exposure tool for projecting an image to a target surface, said exposure tool comprising a control unit for controlling exposure projections, said control unit at least partly being included in the projection space of the said exposure tool, and being provided with control data by means of light signals, said light signals being coupled in to said control unit by using a free space optical interconnect comprising modulated light beams that are emitted to a light sensitive part of said control unit, wherein the modulated light beams are coupled in to said light sensitive part using a holed mirror for on axis incidence of said light beams on said light sensitive part, the hole or, alternatively, holes of said mirror being provided for passage of said exposure projections.

BACKGROUND OF THE INVENTION

The present invention relates to a lithography system for projecting animage pattern on to a target surface such as a wafer, wherein controldata are coupled to a control unit for controlling exposure projectionsby means of light signals, thereby using a free space interconnect, inparticular to a system wherein such control unit is included in closeproximity to or within the projection space, more in particular to amulti-beam mask-less lithography system. The current invention inprinciple relates all the same to charged particle and to lightprojection based lithography systems

Such a system is known, e.g. from the international patent publicationWO2004038509 in the name of Applicant, i.e. from the particularembodiment provided by FIG. 14 thereof. The known system comprises acomputer system for providing pattern data of an image to be projectedby a so called beam column for projecting charged particles, inparticular electrons on to a target surface such as a wafer and aninspection tool. The beam column comprises a vacuum chamber in which oneor more charged particle sources are accommodated, which emit particlesin a manner known per se, using amongst others an electric field forwithdrawing particles from said source or sources.

The beam column further comprises charged particle optic means forconverging an emitted bundle of charged particles, for splitting up thesame into a multiplicity of charged particle beams, further referred toas writing beams, and forming exposure projections. A control unit forcontrolling the exposure projections is included in the form of chargedparticle optical means for shaping or directing such writing beams, hereshowing a blanker optical part or modulator array comprising blankingdeflectors, as well as a writing deflector array for deflecting writingbeams for the purpose writing of a pattern using writing beams notblanked by said blanking deflectors.

The blanker optic part, known per se, e.g. from international patentpublication WO2004107050 in the name of Applicant, deflects, dependingon a computer provided signal a writing beam away from a straighttrajectory parallel with other writing beams, to such amount ofinclination that no part of the writing beam effectively passes theopening provided for each writing beam in a stopping plate, therebyeffecting an “off” state of the particular writing beam.

All optic parts in the beam column are shaped with an array of openings,the openings of the separate parts being mutually aligned so as toenable the passage of a writing beam in said column towards said targetsurface in a controlled manner. The known mask-less multi-beam system isfurther typically provided with blanking deflectors having both thesource and the target surface arranged in a conjugate plane thereof,i.e. it may easily be combined with the subject matter ofWO2004/0819010. In this manner the lithography system favourablyrealizes an optimal brightness of the source on the target surface.Also, in this manner a minimum amount of space is required for theblanker array.

The target surface for a writing beam is held on a stage included in thebeam column. The stage, induced by an electronic control unit of thesystem, moves together with said surface perpendicularly relative tosaid emitted writing bundles, preferably solely in a directiontransverse to a direction in which such writing bundles are finallydeflected for writing purposes. Writing of a pattern by the knownlithography system is thus effected by the combination of relativemovement of the target surface and a timed “on” and “off” switching of awriting beam by said blanker optics upon signalling by said controlunit, more in particular by a so-called pattern streamer thereof.

Signalling for on/off switching, i.e. modulating of a writing beam is inthe related known system performed by using light optics. The blankeroptics thereto comprises light sensitive parts such as photodiodes, forreceiving light signals, which are converted into electronic signals,e.g. applying the measures as provided by the international patentpublication WO2005010618 in the name of Applicant. The light signals areproduced by electronic to light conversion by said control unit for thesystem, and are transported to the beam column by means an opticalcarrier, in casu a bundle of glass fibres that finally projects from“e.g. a transparent part of the vacuum boundary”. Light signals areprojected to said blanker optics using a lens system, which in the knownsystem is disclosed to be comprised of a converging lens located inbetween a transmitter part and the light sensitive parts of deflectorsincluded in the blanker optic part. The arrangement of deflector, lightsensitive parts and light to electric conversion is produced using bothso-called MEMS- and (Bi-) CMOS-technology. So as to prevent the use ofmirroring parts, in the related known system the signalling light beamsare projected from a far upper side relative to the blanking optic part,so as to achieve an angle of incidence of the pattern informationcarrying light signals on the light sensitive elements, as small aspossible. The publication in which the related embodiment is comprised,teaches however, that other locations of projection may be realised whenusing mirrors for correcting the larger angles of incidence occurring atmost of such alternative locations.

Although general set up of the above described lithography system hasproven to be satisfactorily, drawbacks are noticed at the obliqueillumination system disclosed, in that it suffers from non-optimaltransmission of light, at least less than expected and in that itsuffers from relatively large aberrations. The present inventiontherefore seeks to improve the known mask-less multi-beam lithographysystem in general, however, in particular as to the light optics system(LOS) thereof. The present invention further has for an object toimprove the lithography system by either by increasing the lighttransmission efficiency thereof and/or by reducing the chance ofaberrations in the light optic part thereof.

SUMMARY OF THE INVENTION

The present invention solves, at least to a significant extendeliminates the above said problems encountered in the lithographysystems using a mirror for redirecting light beams, provided with one ormore holes for letting through exposure, e.g. writing projections ofsaid lithography system part. In particular a said free space opticalinterconnect of such systems according to the invention comprises aholey, i.e. holed mirror incorporated in the projection trajectory ofsaid plurality of writing beams, wherein said mirror is arrangedrelative to said emitter part and said light sensitive elements torealize an on-axis, i.e. an at least virtually perpendicular incidenceof said light beams on said light sensitive elements, said mirror beingprovided with at least one hole allowing passage of one or more of saidwriting beams.

Alternatively provided, in accordance with further insight underlyingthe present invention, a lithography system is attained, in which anelectronic image pattern is delivered to a exposure tool for projectingan image to a target surface, said exposure tool comprising a controlunit for controlling exposure projections, said control unit at leastpartly being included in the projection space of the said exposure tool,and being provided with control data by means of light signals, saidlight signals being coupled in to said control unit by using a freespace optical interconnect comprising modulated light beams that areemitted to a light sensitive part of said control unit, wherein themodulated light beams are coupled in to said light sensitive part usingholed, alternatively denoted holey mirror for on axis incidence of saidlight beams on said light sensitive part, the one or more holes of saidmirror being provided for passage of said exposure projections.

Using a system according to the present invention minimizes the presenceof aberrations by remaining on-axis at projection of light signals,without, at least noticeably interfering with, i.e. hampering theexposure projections of the exposure tool of the lithography system.With the presently claimed solution, the invention is realized in a new,in advance expectedly impossible, though at hindsight relatively simpleto perform highly favorable manner.

The various aspects and features described and shown in thespecification can be applied, individually, wherever possible. Theseindividual aspects, in particular the aspects and features described inthe attached dependent claims, can be made subject of divisional patentapplications.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be further elucidated by way of example in thefollowing embodiments of a mask-less lithography system according to thecurrent invention, shown in the attached drawings in which:

FIG. 1 is a schematic representation of a the prior art lithographysystem from which the present invention departs;

FIG. 2 is a schematic representation of an improved light optics systemfor the known lithography system according to a first embodiment;

FIG. 3 is a schematic representation of a structural arrangement for thelight optic system of FIG. 2 in the lithography system; and

FIG. 4 is a schematic representation of an improved light optics systemfor the known lithography system according to a second embodiment.

In the figures, corresponding structural features, i.e. at leastfunctionally, are referred to by identical reference numbers.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 represents an overall side view of the prior art lithographysystem that is improved by the current invention, in which at lightemitter, or modulation means ends 2 of a light carrier Fb, in caseembodied by optical fibers Fb, light beams 8 are projected on modulatorarray 24 using an optical system, represented by lenses 54. Modulatedlight beams 8 from each optical fiber end are projected on a lightsensitive element, i.e. light sensitive part of a modulator of saidmodulator array 24. In particular, ends of the fibers Fb are projectedon the modulator array. Each light beam 8 holds a part of the patterndata for controlling one or more modulators, the modulation thereofforming a signaling system for transferring pattern data based modulatorarray instructions for realizing a desired image on said target surface.

FIG. 1 also shows a beam generator 50, which generates a divergingcharged particle beam 51, in this example an electron beam. Using anoptical system 52, in casu an electron optical system, this beam 51 isshaped into a parallel beam. The parallel beam 51 impinges on beamsplitter 53, resulting in a plurality of substantially parallel writingbeams 22, directed to modulation array 24, alternatively denoted blankerarray.

Using modulators in the modulation array 24, comprising electrostaticdeflector elements, writing beams 27 are deflected away from the opticalaxis of the litho system, and writing beams 28 pass the modulatorsundeflected.

Using a beam stop array 25, the deflected writing beams 27 are stopped.The writing beams 28 passing stop array 25 are deflected at deflectorarray 56 in a first writing direction, and the cross section of eachbeamlet is reduced using projection lenses 55. During writing, thetarget surface 49 moves with respect to the rest of the system in asecond writing direction.

The lithography system furthermore comprises a control unit 60comprising data storage 61, a read out unit 62 and data converter 63,including a so-called pattern streamer. The control unit 60 is locatedremote from the rest of the system, for instance outside the inner partof a clean room. Using optical fibers Fb, modulated light beams 8holding pattern data are transmitted to a projector 54 which projectsthe ends of the fibers on to the modulation array 24.

FIG. 2 figuratively represents the light optic system of the improvedlithography system according to a first embodiment. It entails the useof a holey mirror 104, which is applied for realizing an in-axisincidence of light beams 8 on the light sensitive elements of modulatorarray 24. The holey mirror thereto comprises one relatively large holethrough which all for blanking deflected writing beams 27 and allundeflected writing beams 28 may pass, or a plurality of relativelysmall holes 105, one for each deflected or undeflected writing beam.According to preference, the mirror 104 comprises a substantially flatreflecting surface which is included in the system under angle of 45degrees, so that while maintaining perpendicular incidence of lightbeams 8 on modulator 24, an axially minimal amount of space is requiredfor the light optic system. With such minimized axial space requirement,design freedom is attained for locating the LOS either to the upper, orto the bottom side of the modulator array 24, which in turn enhancesmanufacturing freedom of the array 24, which is a highly complex part,manufactured at using CMOS and MEMS technology. With the use of a holeymirror 104, a focusing lens 106, preferably embodied by a lens systemperforming a focusing function, is included close as possible to thelatter, at least closer to the mirror than to the fiber ends 2. Bylocating said focusing lens 106 in close proximity of the holey mirror104, it is favorably realized that the holey mirror can be appliedwithout undue loss in light signal intensity, which might otherwise bedue to the presence of holes 105.

The array of fiber ends 2 are in accordance with the present inventioncompleted with a micro lens array 101, forming a virtual fiber array103, in fact an array of spots in the focal plane for the micro lenses101. In line with a particular and independent aspect of the invention,a micro lens of the micro lens array 101 here according to preferredembodiment performs a magnifying, function on the light signalstransmitted by a particular fiber of the fiber array Fb. The lens systemaccording to the present invention thus sets forth a dual image systemcomprising a magnification of each signal by means of a micro-lens, anda subsequent focusing of the signal by means of said lens 106, common toall of the emitted light signals. In this manner favorably, independenceis attained in setting, in casu increasing an effective spot size ofeach fibre, and setting, in casu decreasing a fiber pitch.

As to the first effect hereabove, it is according to the presentinvention preferred to cover an area as large as possible of a lightsensitive element, so as to obviate the need for strong focus of thelight signal 8, thereby reducing the chance of aberration and therebyreducing the need for further optical elements, which enhances thetransmission of light, i.e. reduces the loss thereof. The desired andcreated light spot is not much larger than the light sensitive area soas to minimize loss of light by projecting light on surrounding, inertparts. This arrangement implies however that the projection of light isrelatively sensitive for positioning errors of a light beam 8, in thatsmall displacement thereof implies a reduction in the amount of lightthan is received by the relevant light sensitive element, e.g.photodiode. Thus, by sizing the incidence spot 24 i larger, but not muchlarger than the light sensitive area, it is according to the inventionprevented that expensive or complex optical elements are required in thefree space interconnect of the LOS, while on the other hand sensitivityas to misalignment of the incident light beam part is reasonablyreduced. In this respect misalignment may be due to actual conditions ofthe litho system, to structural inaccuracy, or to a combination thereof.As to the second effect mentioned here above, the pitch of the ends offibers Fb is incompatible with, in particular larger than the pitch ofthe light sensitive elements on the modulator array 24, unless undue,and consequently uneconomic manufacturing efforts are made. With thepresent dual lens and dual imaging system independence in setting bothparameters is attained in a favorable manner.

FIG. 3 represents the arrangement for preferred incorporation of thelight optics system described along FIG. 2, in the lithography system,according to the invention. It shows a holder 24S for the abovementioned blanker or modulator array 24, by means of which holder themodulator array 24 is placed in a charged particle column. Such chargedparticle column is, together with the holder for holding a wafer orother kind of target surface, included in a housing Hv by means of whicha vacuum condition for said column and target stage is realized. Thearray of fibers Fb is fed through an opening in a demountable part ofsaid housing Hv, here by using a significant amount of vacuum compatiblesealing material for realizing an air tight sealing of the fibres insaid opening. An inner housing end part Fbv of said fibers is therebyalso to a significant extend secured from outside mechanical impulsesthat might act thereon. The end part Fbv of the array of fibers is atits end 2 further secured mechanically to a housing Hl for the lens andmirror part of the light optics system. In turn the housing Hl issecured to said modulator array holder 24S. In this manner it is in afavorable, mechanical manner secured that the positions of the fiberends 2 and the modulator array, in particular the light sensitive areasthereof are fixed relative to one another. In turn, the array holder 24Sis connected to a not depicted frame for elements such as collimator 52,and splitter 53, and as further discussed under FIG. 1, constituting thecharged particle column.

As illustration in one dimension in FIG. 3, the holey mirror 104 coversthe entire area of a modulator array, while in the same manner the lens106 covers the entire area of the tilted mirror 104. The lens 106 isthereby incorporated axially in close proximity to the holder 24S.

It may be clear from the above, that the principles of the dual lenssystem, mechanical fixation of a lens housing Hl to the blanker 24 andthe specific application of a holey mirror 104 may all be appliedindependently from one another. Further to the latter, the principle ofdual imaging can be applied while using an off-axis projection insteadof the presently preferred perpendicular projection.

FIG. 4 figuratively represents the light optic system of the improvedlithography system according to a second embodiment. It entails the useof a holey mirror 107, which is applied for realizing an in-axisincidence of light beams 8 on the light sensitive elements of modulatorarray 24. The holey mirror thereto comprises one relatively large hole108 through which all for blanking deflected writing beams 27 and allundeflected writing beams 28 may pass, or a plurality of relativelysmall holes, one for each deflected or undeflected writing beam.According to preference, the mirror 104 comprises a focussing reflectingsurface, said reflecting surface in particular is placed at an angle forreflecting the incident light beams 8 towards the modulator 24 and saidreflecting surface in particular being a concave surface forsimultaneous focussing the incident light beams 8 onto the modulator 24.

With the use of a holey mirror with a focussing reflecting surface 107,a focusing lens 106, may be omitted. It is favourably realized that anyloss in light signal intensity, in particular due to reflections at thesurfaces of the focussing lens 106, can be further reduced.

Furthermore, it is realized that the focussing element in this secondembodiment, in particular the concave reflecting surface of the holeymirror 107, can be much closer to the modulator array 24, than the lens106 in the first embodiment. Due to this close distance, the lightoptical system of this second embodiment can be designed with a largernumerical aperture and thus with an increased resolving power of thelight optical system.

Also in the second embodiment of FIG. 4, the array of fiber ends 2 arecompleted with a micro lens array 101, forming a virtual fiber array103, in fact an array of spots in the focal plane for the micro lenses101. A micro lens of the micro lens array 101 performs a magnifyingfunction on the light signals transmitted by a particular fiber of thefiber array Fb. The concave reflecting surface of the holey mirror 107according to the second embodiment thus sets forth a dual image systemcomprising a magnification of each signal by means of a micro-lens, anda subsequent focusing of the signal by means of said concave reflectingsurface of the holey mirror 107, common to all of the emitted lightsignals.

Furthermore, it is realized that a holey mirror with a focussingreflecting surface 107 as shown in FIG. 4 may also be combined with afocussing lens 106 as shown in FIG. 3. In this case the focussingelement 106, 107 comprises two optical parts and both optical parts maycontribute to the focussing effect and/or can be used to further reduceoptical aberrations.

Apart from the concepts and all pertaining details as described in thepreceding the invention also relates to all features as defined in thefollowing set of claims as well as to all details as may be directly andunambiguously be derived by one skilled in the art from the abovementioned figures, related to the invention. In the following set ofclaims, rather than fixating the meaning of a preceding term, anyreference numbers corresponding to structures in the figures are forreason of support at reading the claim, included solely as an exemplarymeaning of said preceding term.

1. A lithography system in which an electronic image pattern isdelivered to a exposure tool for projecting an image to a targetsurface, said exposure tool comprising a control unit for controllingexposure projections, said control unit at least partly being includedin the projection space of the said exposure tool, and being providedwith control data by means of light signals, said light signals beingcoupled in to said control unit by using a free space opticalinterconnect comprising modulated light beams that are emitted to alight sensitive part of said control unit, wherein the modulated lightbeams are coupled in to said light sensitive part using a holed mirrorfor on axis incidence of said light beams on said light sensitive part,the hole or, alternatively, holes of said mirror being provided forpassage of said exposure projections.
 2. A lithography system, inparticular according to claim 1, in which an electronic image pattern isdelivered to an exposure tool formed by a writing tool by means of lightprojection, utilizing an exposure projection, in particular a multi beamsystem for mask-less projection of a pattern on to an exposure surface,comprising a vacuum housing within which such writing tool isincorporated, a multi beam projection source being present, creating aplurality of writing beams for writing said pattern, which writing beamsare directed to an blanker array comprising a control unit withindividual controllers such as electrostatic blanker deflectors forindividually controlling a writing beam in accordance received patterninformation, in particular deflecting a writing beam or not, to a beamstopping part, a light optical system comprising light transmittingparts being present for transmitting pattern information signals to suchcontrollers, in particular blanker deflectors, which controllerscomprise light sensitive elements for receiving such modulated lightbeams, such light sensitive elements preferably being accommodatedwithin near vicinity of the deflectors, said light optical systemcomprising a free space optical interconnect, forming a light opticaldata carrier system, transmitting pattern data carrying, modulated lightbeams towards said controllers, which free space optical interconnectcomprises an emitter part emitting free space interconnect, pattern datacarrying light beams to said light sensitive elements, wherein said freespace optical interconnect comprises a holey mirror, incorporated in theprojection trajectory of said plurality of writing beams, said mirrorbeing arranged relative to said emitter part and said light sensitiveelements to realize an on-axis incidence of said light beams on saidlight sensitive elements, and said mirror being provided with at leastone hole allowing passage of one or more of said writing beams.
 3. Asystem according to claim 1, in which an emitting part is incorporatedto emit said light beams at least virtually perpendicular relative to adirection of said exposure projection.
 4. A system according to claim 1,in which said free space interconnect is included at a down stream sideof the control unit.
 5. A system according to claim 1, in which saidfree space interconnect, including an emitter and said holey mirror isincluded in a housing that is mechanically connected to the controlunit, in particular a blanker array, more in particular via a holdertherefore.
 6. A system according to claim 1, in which a focusing lens isincorporated in said free space optical interconnect in near proximityto said holey mirror, in particular significantly nearer to said mirrorthan to said emitter, said lens in particular being common to all of thelight beams emitted by said emitter.
 7. A system according to claim 1,in which said holey mirror comprises a focussing reflecting surface,said reflecting surface in particular being a concave surface, and saidmirror in particular being common to all of the light beams emitted bysaid emitter.
 8. A system according to claim 1, in which a micro lens isincorporated in said free space optical interconnect, in particularthereby forming said emitter, in close proximity to a light carrier end,in particular significantly closer to said carrier end than to saidholey mirror, in particular each light carrier composing part such as anoptic fiber end being provided with a micro lens.
 9. A system accordingto claim 1, wherein the free space optical interconnect comprises amicro lens and a focusing lens common to a possible plurality ofmicro-lens completed fibers, the micro lens therein magnifying a fibertransmitted light signal, and the focusing lens de-magnifying theentirety of light signals transmitted by said possible plurality offibers.
 10. A system according to claim 1, wherein said free spaceoptical interconnect is included in between a control unit formed by ablanker array for blanking writing beams, and a stopping plate forstopping writing beams deflected by said blanker array.
 11. A systemaccording to claim 1, wherein one or more light signal carriers are fedthrough a vacuum wall for the exposure tool using vacuum compatiblesealing material, and are with end parts thereof subsequentlymechanically coupled to a free space optical connect housing located ina vacuum space for the charged particle beam column.
 12. A lithographysystem in which an electronic image pattern is delivered to a writingtool thereof, by projection of modulated, i.e. data carrying light beams(8) to said writing tool, and comprising a free space opticalinterconnect for finally delivering said image pattern to said writingtool, wherein said system, as a part of said free space opticalinterconnect, comprises a holed mirror with one or more holes includedin said writing tool, for directing said light beams in the direction ofprojection of said writing tool, thereby allowing passage of saidwriting tool projection through said hole or holes.
 13. A systemaccording to claim 12, wherein said writing tool preferably utilizing amulti beam system for preferably mask-less projection of a pattern on toan exposure surface, comprising a vacuum housing within which suchlithographic system is incorporated,
 14. Method of projecting lightbeams into a lithography system part, using a mirror for redirectinglight beams, provided with one or more holes for letting through writingprojections of said lithography system part.